Jeffro...Obviously chronology is a passion of yours. Clearly you have spent a great deal of time on this topic and I'm not suggesting what you have done was worthless. However, I've read a number of well argued articles who similarly found ways to work the math with the objective of defending Bible literalness. IMO, and that is all it is, the point is mute. If you are correct that the 70 year topos, while referring to slightly different things for different authors, can be understood through various math formulas to be close to literal 70 years I'll not debate your numbers. You are making the point that the oversimplified interpretation of the WT or others are certainly not correct and cannot by any stretch be an anchor date for scaffolding a church upon.
As I see it, there are just toooooo many variables and potential starting and ending points to convince me that any calculation is the last word in interpreting exactly what some ancient cryptic mystics meant. For me those esoteric and peculiar usages by both Yahwists and non-Yahwists combined with the prolific numeric symbolism present in the OT add up to the expression resembling a figure of speech or trope. 7 times 10 =70. A sacred number times a sacred number equals a sacred number. Why 70 years defined as a typical lifespan? Why not 71? Why 70 nations, why 70 sons............
Never in a million years, once in a blue moon, in a coons age, a month of Sundays, years on end, light years away, These are modern proxies, void of any sacredness they still mean something other than what a literalist 2500 years from might assume.